Tutorial by Examples: di

Optionals must be unwrapped before they can be used in most expressions. if let is an optional binding, which succeeds if the optional value was not nil: let num: Int? = 10 // or: let num: Int? = nil if let unwrappedNum = num { // num has type Int?; unwrappedNum has type Int print(&quo...

var favoriteColors: Set = ["Red", "Blue", "Green"] //favoriteColors = {"Blue", "Green", "Red"} You can use the insert(_:) method to add a new item into a set. favoriteColors.insert("Orange") //favoriteColors = {"Red&q...

Import the ElementTree object, open the relevant .xml file and get the root tag: import xml.etree.ElementTree as ET tree = ET.parse("yourXMLfile.xml") root = tree.getroot() There are a few ways to search through the tree. First is by iteration: for child in root: print(child.ta...

(Note: All examples using let are also valid for const) var is available in all versions of JavaScript, while let and const are part of ECMAScript 6 and only available in some newer browsers. var is scoped to the containing function or the global space, depending when it is declared: var x = 4; /...

Final classes When used in a class declaration, the final modifier prevents other classes from being declared that extend the class. A final class is a "leaf" class in the inheritance class hierarchy. // This declares a final class final class MyFinalClass { /* some code */ } ...

A dictionary is an example of a key value store also known as Mapping in Python. It allows you to store and retrieve elements by referencing a key. As dictionaries are referenced by key, they have very fast lookups. As they are primarily used for referencing items by key, they are not sorted. crea...

const fs = require('fs'); // Read the contents of the directory /usr/local/bin asynchronously. // The callback will be invoked once the operation has either completed // or failed. fs.readdir('/usr/local/bin', (err, files) => { // On error, show it and return if(err) return console.er...

Use Case CASE can be used in conjunction with SUM to return a count of only those items matching a pre-defined condition. (This is similar to COUNTIF in Excel.) The trick is to return binary results indicating matches, so the "1"s returned for matching entries can be summed for a count o...

project/jni/main.c #include <stdio.h> #include <unistd.h> int main(void) { printf("Hello world!\n"); return 0; } project/jni/Android.mk LOCAL_PATH := $(call my-dir) include $(CLEAR_VARS) LOCAL_MODULE := hello_world LOCAL_SRC_FILES := main.c include $(BU...

A useful feature of namespaces is that you can expand them (add members to it). namespace Foo { void bar() {} } //some other stuff namespace Foo { void bar2() {} }

The keyword 'using' has three flavors. Combined with keyword 'namespace' you write a 'using directive': If you don't want to write Foo:: in front of every stuff in the namespace Foo, you can use using namespace Foo; to import every single thing out of Foo. namespace Foo { void bar() {} ...

There are several ways to read data from a file. If you know how the data is formatted, you can use the stream extraction operator (>>). Let's assume you have a file named foo.txt which contains the following data: John Doe 25 4 6 1987 Jane Doe 15 5 24 1976 Then you can use the following...

collections.defaultdict(default_factory) returns a subclass of dict that has a default value for missing keys. The argument should be a function that returns the default value when called with no arguments. If there is nothing passed, it defaults to None. >>> state_capitals = collections.d...

jQuery code is often wrapped in jQuery(function($) { ... }); so that it only runs after the DOM has finished loading. <script type="text/javascript"> jQuery(function($) { // this will set the div's text to "Hello". $("#myDiv").text("Hello"...

The value of a cookie can be modified by resetting the cookie setcookie("user", "John", time() + 86400, "/"); // assuming there is a "user" cookie already Cookies are part of the HTTP header, so setcookie() must be called before any output is sent to the...

cat < file.txt Output is same as cat file.txt, but it reads the contents of the file from standard input instead of directly from the file. printf "first line\nSecond line\n" | cat -n The echo command before | outputs two lines. The cat command acts on the output to add line num...

Function overloading is having multiple functions declared in the same scope with the exact same name exist in the same place (known as scope) differing only in their signature, meaning the arguments they accept. Suppose you are writing a series of functions for generalized printing capabilities, b...

To get started with the jQuery UI library, you'll need to add the jQuery script, the jQuery UI script, and the jQuery UI stylesheet to your HTML. First, download jQuery UI; choose the features you need on the download page. Unzip your download, and put jquery-ui.css and jquery-ui.js (and jquery.js)...

Using the threading module, a new thread of execution may be started by creating a new threading.Thread and assigning it a function to execute: import threading def foo(): print "Hello threading!" my_thread = threading.Thread(target=foo) The target parameter references the fun...

A module can be "imported", or otherwise "required" by the require() function. For example, to load the http module that ships with Node.js, the following can be used: const http = require('http'); Aside from modules that are shipped with the runtime, you can also require mod...